The present invention relates to an image signal generating apparatus, an image display unit, and a control method for an image display unit useful in, for example, a personal computer system having a plurality of image display units.
Examples of image display units to which the invention is applicable include liquid crystal display (LCD) units, cathode-ray tube (CRT) units, digital micromirror device (DMD) units, plasma display panel (PDP) units, and field-emission display (FED) units.
As a conventional example of a system with multiple image display units, FIG. 1 shows a system in which a single image signal generating unit 101 supplies separate image signals through separate cables to four image display units 102 simultaneously. The image signals are generated separately by four image signal generators 103. The image signal generators 103 comprise, for example, hardware circuits disposed on one or more expansion cards installed in a personal computer. Each image signal generator 103 has a separate cable connector. Each image signal, and each image display unit 102, has a standard resolution such as seven hundred sixty-eight lines with one thousand twenty-four picture elements or pixels per line (1024xc3x97768 pixels). The four image signals may be combined, as shown, to form a single image with a higher resolution (2048xc3x971536 pixels).
A problem with this conventional system is that each time an image display unit is added to the system configuration, another image signal generator 103 and another interconnecting cable are required. The number of image display units 102 that can be controlled is thus limited by the expansion capacity of the personal computer. Often, the personal computer lacks space for an adequate number of display signal generators 103, or for an adequate number of cable connectors.
FIG. 2 shows another conventional example, in which the image signal generating unit 101 has a single image signal generator 103 that generates a high-resolution signal (for example, a signal with a resolution of 2048xc3x971536 pixels). The high-resolution signal is distributed to four image display units 102, each having a lower resolution (1024xc3x97768 pixels, for example). Each image display unit 102 displays one quadrant of the image.
A problem in this configuration is that high-speed digital-to-analog (D/A) and analog-to-digital (A/D) converters are required to generate and process the high-resolution image signal. High-speed D/A and A/D converters are expensive, and their performance limits both the attainable resolution and the quality of the displayed image. In practice, the limited performance of available D/A and A/D converters tends to degrade the image quality.
An object of the present invention is to enable a single image signal generating unit, generating a standard image signal, to display different images on different image display units.
Another object is to enable the number of image display units coupled to the image signal generating unit to be increased easily.
A further object is to enable a user to use one image display unit for normal input and editing work, while referring to reference images displayed on other image display units.
An image signal generating unit or apparatus according to the present invention comprises an image signal generator generating an image signal, and an indexer adding an index signal to the image signal, replacing part of the image signal. The index signal designates an image display unit by which the image signal is to be displayed.
An image display unit according to the present invention comprises an image signal receiving circuit, a frame selection unit, and an image display apparatus. The image signal receiving circuit receives a composite signal including an image signal divided into frames, a synchronizing signal, and an index signal. The frame selection unit selects certain frames of the image signal according to the index signal. The image display apparatus displays the selected frames. The frame selection unit preferably includes an image memory for storing the most recently selected frame.
A method of controlling an image display unit according to the present invention comprises the steps of:
(a) receiving an image signal divided into frames;
(b) selecting certain frames according to an index signal included in the image signal; and
(c) displaying the selected frames.
The invention enables the image signal generating unit to direct different images to different image display units by switching the value of an index signal embedded in a standard image signal.
The image signal generating unit outputs a single image signal, the format of which does not change when further image display units are added, so image display units can be added easily.
Image display units having image memories can display reference images without interrupting normal input and editing operations.